The present invention relates to a magneto-optical recording medium for use as a magneto-optical memory, a magnetic recording and display element and so forth and, more particularly, to improvement in a magnetic thin film recording medium which has an easy axis of magnetization in a direction perpendicular to the film surface and permits recording of information by forming an inverted magnetic domain of a circular or arbitrary configuration and readout of the information through utilization of the magnetic Kerr effect or like magneto-optic effect.
With ferromagnetic thin films having the easy axis of magnetization in a direction perpendicular to the film surface, it is possible to form small inverted magnetic domains which have a magnetic pole reverse from a uniform magnetization polarity in the film surface uniformly magnetized with south or north magnetic pole. By making the presence and absence of the inverted domains correspond to binary information "1" and "0", respectively, such ferromagnetic thin films can be used as high density magnetic recording media. Of such ferromagnetic thin films, thin films which have a large coercive force at room temperature and have a Curie point or magnetic compensation temperature relatively close to room temperature permit recording of information by forming inverted magnetic domains at arbitrary positions with a light beam through utilization of the Curie point or magnetic compensation temperature; therefore, they are generally used as beam addressable files.
Conventionally known ferromagnetic thin films which have an easy axis of magnetization in a direction perpendicular to the film surface and can be used as beam addressable files are polycrystalline metal thin films represented by MnBi, amorphous metal thin films, such as Gd-Co, Gd-Fe, Tb-Fe, Dy-Fe, etc., and compound single crystal thin films represented by GIG Gadolinium Iron Garmet.
Furthermore, amorphous alloy thin films containing 15 to 30% atoms of Tb or Dy, such as TbFe and DyFe, have been proposed as new magnetic thin film recording media. On account of the following merits, the amorphous alloy thin films are regarded as promising as magneto-optical recording media.
(1) Since they have the easy axis of magnetization in the direction perpendicular to the film surface and have a large coercive force of several kilooersteds at room temperature, information can be recorded with high density and the recorded information is very stable.
(2) The coercive force is large so that magnetic domain of desired configuration can be written.
(3) Since they have a large coercive force over a wide range of composition and have excellent characteristics as recording media over a wide range of composition, they need not be severely restricted in composition and can be readily fabricated at a good yield rate.
(4) Since the Curie point is as low as 120.degree. C. in the TbFe and 60.degree. C. in the DyFe, a thermal writing operation utilizing the Curie point can be effected with very small energy.
However, the amorphous alloy thin films, such as the TbFe, DyFe, etc., have the following drawbacks: That is to say, it is true that a low Curie point permits a writing operation with small energy, but it impairs the SN ratio in case of reading out information by light.